Traditional worldwide radio frequency (RF) broadband communications systems may employ geosynchronous (GEO) satellite vehicles (SAT) to relay communication signals to and from an airborne station. This distant GEO SAT relay is physically limited by line of sight and range. Current GEO SAT orbits are in the range of 23,300 miles above the equator and may inherently possess an approximate 300 millisecond (ms) one way travel time in signal transmission from a point on the surface of the earth, relayed from the GEO SAT, to an airborne station above the surface of the earth.
Current video conferencing systems demand less than 100 ms latency in signal transmission to effectively operate without a noticeable delay for the user. This 100 ms benchmark has proven to be a requirement for most video conferencing applications in use. Practical Internet Protocol (IP) based airborne video conferencing systems may be limited by severe GEO SAT latencies which, depending on range and the ground network design, may reach as much as a second to several seconds of signal travel time making the video conference experience undesirable and difficult. A user attempting to video conference over a high latency GEO SAT system without being trained in the use of such a system may result in one user talking during the time the opposite user is talking.
This 100 ms benchmark is physically beyond current capabilities of GEO SAT relay systems. The cumbersome GEO SAT delay may have proven tolerable in the past. However, with current communications systems employed onboard airborne vehicles and within portable devices, this level of latency may be unacceptable to users. Specifically, transmission time of radio signals within the free space distance of a GEO SAT will always exceed the discernable 100 ms threshold for successful bi-directional audio and video teleconferencing.
In addition, GEO SAT systems require a large antenna element mounted onboard the airborne station (e.g., an aircraft) to physically connect with the distant GEO SAT. The large scale of the GEO SAT communications antenna element physically limits the size of the platform on which the GEO SAT communications system may be installed. In some cases, traditional airborne GEO SAT antenna elements may require a diameter of as much as three to four feet of horizontal space on the upper fuselage of the airborne vehicle to enable the gain to be sufficient. This spatial requirement eliminates smaller aircraft (which may have fuselage diameters as small as 4.5 feet) from consideration for a satellite based communications system. Large antennas designs limit effect the aircraft aerodynamics and reduce the effective range, a highly competitive factor among aircraft manufacturers.
Additionally, while operating above and below approximately 70 degrees of north and south latitude, GEO SAT based communications systems onboard airborne vehicles begin to lose their visibility to the geosynchronous belt due to the physical low look angle of the airborne antenna elements at that latitude. This limitation may eliminate service availability and also be intolerable to specific users routinely flying in the polar areas of the world.
Traditional Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) SAT constellations may operate constrained by spectrum, by SAT population (beam density), by bandwidth, or a combination of all three. These deployed constellations are inherently constrained by bandwidth and spacecraft beam density to enable lower bit rate (LBR) video communication at 100s of kilobits to low megabit channel averages. They are unable to offer the bandwidth and latency necessary for higher definition, multi-user, multi-megabit video conferencing.
Therefore, a need remains for a markedly greater broadband system introducing novel elements onboard the airborne station coupled with a higher density, broadband LEO SAT constellation offering a network architecture configured for real time video conferencing of less than 100 ms in communications available to the airborne station. Further there is a need for the system to operate seamlessly and globally at the lowest cost.